In manufacturing an electronic device such as a semiconductor device, various treatments are performed on an object to be processed. Film formation is an example of the treatment performed on the object. Sputtering may be used for the film formation.
As for an electronic device, there has been developed a MRAM (Magnetoresistive Random Access Memory) device having a MTJ (Magnetic Tunnel Junction) structure. In the MTJ structure, a magnesium oxide (MgO) layer may be used as a tunnel barrier layer. The MgO layer is generally formed by the following processes. Mg is deposited on an object to be processed by using a sputtering apparatus having a target made of Mg. Next, the object is transferred to an oxidation apparatus connected to the sputtering apparatus via a vacuum transfer apparatus. Then, Mg is oxidized by exposing the target object to an oxidizing gas in the oxidation apparatus. The formation of the MgO layer is disclosed in, e.g., International Publication No. WO2012/086183.